X-ray camera

ABSTRACT

X-ray camera of the present invention comprises an X-ray irradiation unit, an X-ray image sensor, a controller having a correction factor setting unit, a correction factor storage unit and a correctional operation unit, and a display unit. The X-ray image sensor in the above configuration comprises a sensor such as CCD, TFT, and the like having a scintillator on a surface thereof, and a substrate having the sensor mounted thereon. The correction factor setting unit obtains a value La/Ln by dividing a predetermined brightness reference value La set beforehand by a brightness value Ln of an arbitrary pixel “n”, and sets the obtained value as a correction factor for each pixel. The correction factor storage unit stores the correction factor set by the correction factor setting unit. The correctional operation unit obtains the correction factor from the correction factor storage unit, and performs a corrective operation.

FIELD OF THE INVENTION

The present invention relates to X-ray camera used in medical diagnosis,dentistry, and the like.

BACKGROUND OF THE INVENTION

X-ray camera of the kind known heretofore include:

conventional X-ray camera used in medical diagnosis for takingphotographs of joint regions such as hands and feet, chest, and so on;and

intraoral X-ray camera and panoramic X-ray camera used in dentistry.

As for the method of displaying images, it has been a general practiceto print out X-ray images on films for use as monochrome pictures.

In recent years however, there evolved another method of displaying animage that uses a variety of digital techniques after transferring anX-ray image onto a special fluorescent film.

Some of the techniques proposed for use in the method of displayingimages include:

a CR (Computed Radiography) technique, in which a fluorescent image isread by using laser, and stored as a digital image;

a technique, in which a combination of charge coupled device(hereinafter referred to as “CCD”) and fluorescent material is used toread directly as a digital image in a similar manner as the videophotography; and

a technique, in which a combination of TFT (Thin Film Transistor) paneland photo diode, in combination with fluorescent material is used toread directly as a digital image in a similar manner as the videophotography.

Unlike the case of using films, an X-ray camera that uses the digitaltechniques as above represents a method of expression, in that theequipment accurately reads an X-ray photographic image pixel by pixel,and composes a complete image by realigning again the individual pixeldata obtained therefrom on a display device.

For this reason, any defect of pixels of the CCD, the TFT, and the like,manufacturing dispersion of the reading circuits for individual pixels,and so on are reflected just as they are in the pixel data. This hasbeen the failure peculiar to the digital X-ray photography thatdeteriorates picture quality of display images as typified by slightvariations in brightness.

SUMMARY OF THE INVENTION

The present invention is to solve the foregoing problem of the prior arttechnique, and intended to improve picture quality of X-ray photographicimages.

To achieve the above-described problem, X-ray camera of this inventioncomprises:

an X-ray irradiation unit;

an X-ray image sensor;

a controller comprising a correction factor setting unit, a correctionfactor storage unit, and a correctional operation unit; and

a display unit.

The X-ray image sensor in the above configuration comprises:

a sensor such as CCD, TFT, and the like having a scintillator on asurface of it; and

a substrate having the sensor mounted thereon.

The correction factor setting unit (hereinafter referred to simply as“setting unit”) obtains a value La/Ln for an arbitrary pixel “n” bydividing a predetermined brightness reference value La set beforehand bya brightness value Ln of the arbitrary pixel “n”, and sets the obtainedvalue as a correction factor of each pixel.

The correction factor storage unit (hereinafter referred to simply as“storage unit”) stores the correction factor set by the setting unit.

The correctional operation unit (hereinafter referred to simply as“operation unit”) obtains the correction factor from the storage unit,and performs a corrective operation.

The display unit displays an image, which is corrected by the operationunit.

The X-ray camera of this invention, with the configuration as describedabove, cancels errors in brightness caused by inherent dispersion of thesensors and image detector circuits peculiar to the X-ray camera, bymaking correction of brightness of the image obtained in thephotography, and thereby it can realize substantial improvement inquality of the X-ray image.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration depicting a configuration of X-ray camera of afirst exemplary embodiment;

FIG. 2A is a diagrammatic illustration showing an aspect of taking anX-ray image of a subject 1 serving as a reference;

FIG. 2B is a diagrammatic illustration showing an example of brightnessdistribution of the image of the subject 1 obtained with an X-ray imagesensor 2 along a row of pixels in a one-dimensional direction;

FIG. 3A is a diagrammatic illustration showing an aspect of taking anX-ray image of a model subject;

FIG. 3B is a diagrammatic illustration showing an example of brightnessdistribution of the image, obtained with the X-ray image sensor bytaking photograph of the model of step-wise configuration, along a rowof pixels in a one-dimensional direction;

FIG. 3C is a diagrammatic illustration showing the brightnessdistribution after correction;

FIG. 4 is an illustration depicting an example of another configurationof the controller shown in FIG. 1;

FIG. 5 is a flow chart showing an operational flow of the X-ray cameraof the first exemplary embodiment;

FIG. 6A is an expository illustration depicting operation of X-raycamera having a sensor configuration described in a third exemplaryembodiment;

FIG. 6B is a diagrammatic illustration showing an example of brightnessdistribution of an image, obtained with the X-ray image sensor 2 of thethird exemplary embodiment, along a row of pixels in a one-dimensionaldirection;

FIG. 6C is a diagrammatic illustration showing the brightnessdistribution after corrected according to the third exemplaryembodiment;

FIG. 7A is an expository illustration depicting operation of X-raycamera having a sensor configuration described in a fourth exemplaryembodiment;

FIG. 7B is a diagrammatic illustration showing an example of brightnessdistribution of an image, obtained with the X-ray image sensor 2 of thefourth exemplary embodiment, along a row of pixels in a one-dimensionaldirection; and

FIG. 7C is a diagrammatic illustration showing the brightnessdistribution after corrected according to the fourth exemplaryembodiment.

THE BEST MODE FOR CARRYING OUT THE INVENTION

With reference to accompanying figures, X-ray camera of the presentinvention will be described hereinafter.

First Exemplary Embodiment

Referring now to FIG. 1 through FIG. 5, a first exemplary embodiment ofthis invention is described hereinafter.

FIG. 1 is an illustration depicting a configuration of the X-ray cameraof the first exemplary embodiment of this invention. As shown in FIG. 1,the X-ray camera of the first exemplary embodiment comprises:

an X-ray irradiation unit 100;

an X-ray image sensor 2;

a controller 200 comprising a setting unit 4, a storage unit 5, and anoperation unit 6; and

a display unit 300.

A reference numeral 400 shown in FIG. 1 schematically illustrates asubject for the X-ray equipment.

As shown in FIG. 2A, an X-ray image sensor unit (hereinafter referred tosimply as “sensor unit”) 20 in the above configuration comprises:

an X-ray image sensor (hereinafter referred to simply as “sensor”) 2such as CCD, TFT, and the like having a scintillator on a surface of it(not shown in the figure); and

a substrate 7 having the sensor 2 mounted thereon.

A corrective operation of brightness of a photographed image displayedin the display unit 300 is described now.

FIG. 2A diagrammatically illustrates an aspect of taking an X-ray imageof a reference subject 1. In FIG. 2A, when X rays are irradiated to thereference subject 1, the X rays penetrated through the subject 1 areconverted into light signal by the scintillator (not show in thefigure), and detected as an image by the sensor 2 mounted on thesubstrate 7.

FIG. 2B diagrammatically illustrates an example of brightnessdistribution along a row of pixels in a one-dimensional direction of theimage of the reference subject 1 obtained by the sensor 2.Fundamentally, value of brightness shall be invariant from pixel topixel. However, the value of brightness varies slightly from pixel topixel as shown in FIG. 2B, due to an inherent dispersion of the sensor2, detector circuits (not show in the figure), or the like.

Therefore, the setting unit 4 obtains a value La/Ln for an arbitrarypixel “n” by dividing a predetermined brightness reference value La by abrightness value Ln of the arbitrary pixel “n”, and sets the obtainedvalue as a correction factor of each pixel. Here, the brightnessreference value La is a design value of the sensor 2, and therefore thevalue of brightness that should naturally be output.

The correction factor for each pixel obtained by taking the X-ray imageof the reference subject 1 is stored in the storage unit 5.

Described next pertains to a corrective operation carried out accordingto the correction factor obtained above for brightness of an image takenby X-ray photographing a step-wise configuration model 3, which typifiesa subject body. The step-wise configuration model 3 is composed ofaluminum and the like, to represent a subject body in place of a humanbody.

FIG. 3A diagrammatically illustrates an aspect of taking an X-ray imageof the model serving as a subject body. In FIG. 3A, when X rays areirradiated to the step-wise configuration model 3, the X rays penetratedthrough the step-wise configuration model 3 are converted into lightsignal by the scintillator (not show in the figure), and detected as animage by the sensor 2 mounted on the substrate 7. FIG. 3Bdiagrammatically illustrates an example of brightness distribution alonga row of pixels in a one-dimensional direction of the image obtainedwith the sensor 2 by taking photograph of the step-wise configurationmodel 3. Fundamentally, value of brightness shall be invariant frompixel to pixel. However, the value of brightness varies slightly frompixel to pixel as shown by a line Ln′ in FIG. 3B, due to an inherentdispersion of the X-ray image sensor 2, detector circuits (not show inthe figure), or the like.

Thus, the operation unit 6 obtains the correction factor from thestorage unit 5, and implements a corrective operation by way ofmultiplication with the line Ln′ of FIG. 3B. This operation yields theright brightness value (Ln′×La/Ln) for the image. FIG. 3Cdiagrammatically shows the corrected brightness distribution.

The corrected image is thus displayed in the display unit 300.

With the configuration as described above, the X-ray camera of thisinvention can substantially improve picture quality of the X-ray imageby virtue of canceling errors in brightness caused by inherentdispersion of the sensors and the image detector circuits peculiar tothe X-ray camera, through correction of brightness of the image obtainedin the photography.

In this embodiment, as described above, the predetermined brightnessreference value (design value) La was used to obtain the correctionfactor. However, an average value of brightness of the entire image maybe used as the reference value La. Alternatively, it is also acceptableto use a representative value of brightness of the entire image (e.g., amaximum value, a mean value, a minimum value, and the like) as thereference value. FIG. 4 shows an example of configuration of thecontroller in this case.

A setting unit 4 sets correction factors corresponding to three sorts ofvalues, which are:

an average value of brightness;

a representative value of brightness; and

a predetermined reference brightness value for each pixel of an imageobtained by taking an X-ray photograph of the reference subject. Astorage unit 52 stores the three sorts of correction factors set asabove. When making correction of brightness of an image obtained bytaking an X-ray photograph of a subject body, the operation unit 6obtains a corresponding correction factor among the three sorts ofcorrection factors through a correction factor selection unit 72 in thestorage unit 52.

As described above, brightness characteristic of the X-ray image sensor2 actually in used can be corrected by virtue of making correctionresponsive to dispersion of the individual X-ray image sensor. Anaccuracy of displaying the image can thus be improved. Further, featureof individual operation process determines which one to use between theaverage value and the representative value. In other words, the averagevalue is used when accuracy is required, and the representative value isused when a high-speed processing is needed.

Furthermore, there results in a better improvement of the accuracy whenusing the value obtained from the division as La/Ln for the correctionfactor to be set for each pixel, as compared to the use of a differencelike La−Ln, which can be influenced by intensity of external light,illumination, and so on.

As for a reference subject, it may be appropriate to use a soft-tissueequivalent material such as urethane resin and the like to representmuscles and adipose tissue, or a bone-tissue equivalent material such asepoxy resin, aluminum and the like.

Next, FIG. 5 shows an operational flow of the entire X-ray camera of thefirst exemplary embodiment of this invention.

Upon start of the X-ray camera, a selection is made between settingoperation of a correction factor and photographing of a human body (step1).

If step 1 selects the setting operation of a correction factor at astart of the X-ray camera, the system takes an X-ray photograph of thereference subject 1 (step 2).

The setting unit 4 calculates a correction factor for each pixel basedon brightness data of the image obtained in step 2 (step 3).

The correction factor for each pixel obtained in step 3 is stored in thestorage unit 5 comprised of a semiconductor memory, a hard disk, and thelike (step 4). It returns to the initial state of the system, after thecorrection factor is stored.

If step 1 selects the subject body to be photographed, it takes an X-rayphotograph of the human body (step 5).

The operation unit 6 obtains the correction factor for each pixel fromthe storage unit 5, and carries out a corrective operation based on thebrightness data of the image taken in step 5 (step 6).

The display unit 300 displays the X-ray image after the correctiveoperation is made in step 6 (step 7).

The above steps 2, 3, and 4 can be initiated at any timing to reset thecorrection factor, when the equipment is first installed, when a userdetermines it necessary, and so on. If the correction factor has alreadybeen set and stored, the steps 1, 5, 6, and 7 are normally executed.

Second Exemplary Embodiment

A second exemplary embodiment relates to X-ray camera, which sets pluralsorts of correction factors to be stored, as described in the firstexemplary embodiment. It is so devised as to be capable of selectingwhich correction factor to use among those correction factors stored ina plurality of storage means, according to thickness of a portion of ahuman body to be photographed.

A configuration of a controller 202 of the second exemplary embodimentis analogous to the controller 202 shown in the first exemplaryembodiment. Although there is a slight difference in function of theirrespective configurations, the following description will be made inthis exemplary embodiment with reference to FIG. 4, since they areanalogous in configuration.

The controller 202 of the second exemplary embodiment comprises asetting unit 4, a plurality of storage units 52 capable of storingcorrection factors, a selection unit 72 for selecting among the storageunits 52 a correction factor corresponding to a portion of the subjectto be irradiated with X-rays, and an operation unit 6.

In this exemplary embodiment, a photograph is taken by irradiating Xrays to a reference subject according to a thickness of photographingportion of a human body to be measured, in the same manner as the firstexemplary embodiment.

The setting unit 4 sets correction factors according to the result, inthe same manner as the first exemplary embodiment. The storage units 52then store the correction factors set as above.

When an X-ray photograph is taken for a portion of the subject humanbody, the operation unit 6 obtains a correction factor for each pixelbased on brightness data of the acquired image from one of the storageunits 52 that corresponds to the portion of the subject human body,through the selection unit 72, and carries out a corrective operation.

Th display unit 300 displays the X-ray image after the correctiveoperation is made.

Accordingly, the most appropriate correction factor can be chosenaccording to thickness of the photographing portion of the human body,when the plurality of correction factors having several sorts ofdifferent thicknesses of the reference subject are set and stored.

If photographs are taken for two kinds of equivalent materials, asoft-tissue equivalent material and a bone-tissue equivalent material,for instance, the setting unit 4 sets two sorts of correction factorscorresponding to the respective equivalent materials. The storage units52 store the two sorts of correction factors set as above. When making acorrection of brightness of the image acquired by taking an X rayphotograph of the subject body, the operation unit 6 obtains acorrection factor for each pixel from one of the storage units 52, whichcorresponds to the portion of the subject human body, through theselection unit 72, and carries out the corrective operation.

Th display unit 300 can then display the X-ray image after thecorrective operation is made.

Third Exemplary Embodiment

A third exemplary embodiment relates to X-ray camera for taking an X rayphotograph with a plurality of X-ray image sensors arranged in anoverlapped manner. FIG. 6A shows an example in which a plurality ofsensors are arranged so as to overlap with one another at the analogousportions.

As shown in FIG. 6A, three sets of the X-ray image sensor 2 are arrangedin a manner that an effective image-capture area (i.e. an area normallynarrower than an overall perimeter of the X-ray image sensor) of each ofthe X-ray image sensors overlaps with one another, in order to detect animage without any dropout portion. It is so designed that an imagecaptured by the sensor located at the front side toward the subject istaken for the image of the overlapped portion. When X rays areirradiated, a portion between an effective image-capture area and aperimeter of the front side sensor gives a shadow on an effectiveimage-capture area of the sensor placed behind the front one, as shownin FIG. 6B. This causes a phenomenon of partially decreasing thebrightness only in the area of this shadow. This phenomenon is thelargest problem in the X-ray photography with the plurality of X-rayimage sensors arranged in the overlapped manner.

The X-ray camera of the third exemplary embodiment obtains a correctionfactor for each of arbitrary pixel “n”, and carries out a correctiveoperation for each pixel, in the same manner as described in the firstexemplary embodiment. Accordingly, it is proved effective even when theplurality of sensors, arranged in the overlapped manner, are used as theX-ray image sensor, and satisfactory correction of brightness can beachieved, as shown in FIG. 6C.

Fourth Exemplary Embodiment

A fourth exemplary embodiment relates to X-ray camera for taking an Xray photograph with a plurality of X-ray image sensors arranged in anoverlapped manner. FIG. 7A shows an example in which a plurality ofsensors are arranged in a step-wise manner at the analogous portions.

When X rays are irradiated, a portion between an effective image-capturearea and a perimeter of the front side sensor produces a shadow as shownin FIG. 7B on an effective image-capture area of the sensor placedbehind the front one, in the like reason as the third exemplaryembodiment. This causes a phenomenon of partially decreasing thebrightness only in the area of this shadow. This phenomenon is thelargest problem in the X-ray photography with the plurality of X-rayimage sensors arranged in the overlapped manner.

The X-ray camera of the fourth exemplary embodiment obtains a correctionfactor for each of arbitrary pixel “n”, and carries out a correctiveoperation for each pixel, in the same manner as described in the firstexemplary embodiment. As described, it is proved effective even when theplurality of sensors, arranged in the overlapped manner, are used as theX-ray image sensor, and thereby satisfactory correction of brightnesscan be achieved, as shown in FIG. 7C.

INDUSTRIAL APPLICABILITY

As has been described, the X-ray camera according to this inventioncancels errors in brightness caused by inherent dispersion of thesensors and image detector circuits peculiar to the X-ray camera, byproviding a correctional function for brightness of an image obtained inthe photography, and thereby it can realize substantial improvement inquality of the X-ray image.

Moreover, it provides for a possibility of correcting image qualityprecisely according to the subject and portion being photographed, byallowing selection of a method of calculating the correction factor, anda plural kinds of reference subject to be used for setting thecorrection factor based on a purpose of the photograph.

Accordingly, it is extremely useful for radiographic diagnosis in themedical field.

In addition, it is also adaptable for the correction of brightness inthe overlapped area of sensors, in the case of equipment that uses acombination of plural sensors for the purpose of obtaining a widephotographable area, and therefore it is extremely useful again forradiographic diagnosis in the medical field.

What is claimed is:
 1. An X-ray camera comprising: an X-ray irradiationunit; an X-ray image sensor including an X-ray-to-photo conversiondevice for converting an X-ray radiated from said X-ray irradiation unitto a photo signal for corresponding to an intensity of the X-ray and aphotoelectric conversion device for converting the photo signal to anelectric signal to output brightness data of an image in a unit of apixel; a correction factor setting unit for setting a correction factorbased on electronic image data of a reference subject provided from saidX-ray image sensor which takes an X-ray photograph of the referencesubject; a correction factor storage unit for storing the correctionfactor set in said correction factor setting unit; and a controller forcorrecting the brightness data of the image output from said X-ray imagesensor based on the correction factor to output corrected brightnessdata.
 2. The X-ray camera as set forth in claim 1, wherein saidcorrection factor for improvement of picture quality acquired from thebrightness data of the image obtained by taking the X-ray photograph ofsaid reference subject is set therein for each pixel individually. 3.The X-ray camera as set forth in claim 2, wherein a value acquired bydividing a predetermined brightness reference value with a brightnessvalue of each pixel in the image obtained by taking the X-ray photographof said reference subject is used as a correction factor for said pixel.4. The X-ray camera as set forth in claim 3, wherein said controllercorrects the brightness of each pixel by multiplying a brightness valueof said pixel in the image obtained by taking the X-ray photograph of asubject body by said correction factor of the corresponding pixel. 5.The X-ray camera as set forth in claim 2, wherein a value acquired bydividing an average value of brightness of the image obtained by takingthe X-ray photograph of said reference subject with the brightness valueof each pixel is used as a correction factor for said pixel.
 6. TheX-ray camera as set forth in claim 5, wherein said controller correctsthe brightness of each pixel by multiplying a brightness value of saidpixel in the image obtained by taking the X-ray photograph of saidreference subject by said correction factor of the corresponding pixel.7. The X-ray camera as set forth in claim 2, wherein a value acquired bydividing a representative value of brightness of the image obtained bytaking the X-ray photograph of said reference subject with thebrightness value of each pixel is used as a correction factor for saidpixel.
 8. The X-ray camera as set forth in claim 7, wherein saidcontroller corrects brightness of each pixel by multiplying a brightnessvalue of said pixel in the image obtained by taking the X-ray photographof said reference subject by said correction factor of the correspondingpixel.
 9. The X-ray camera as set forth in claim 2, wherein urethaneresin for typifying a soft-tissue equivalent material representingmuscles and adipose tissue, composed of urethane resin and the like, isused as the reference subject.
 10. The X-ray camera as set forth inclaim 2, wherein any of epoxy resin and aluminum typifying a bone-tissueequivalent material is used as the reference subject.
 11. The X-raycamera as set forth in claim 2 further comprising a correction factorsetting means for setting a correction factor, other than ordinary X-rayphotography, in order to acquire said correction factor, wherein saidX-ray camera can be operated for resetting a correction factor forimprovement of picture quality at an arbitrary timing when saidequipment is first installed, when a user determines it necessary. 12.The X-ray as set forth in claim 1 wherein said correction factor storageunit stores three types of correction factors obtained by dividing eachof three values by a brightness value of each pixel, said three valuesbeing an average value and a representative value of brightness of animage obtained by taking the X-ray photograph of said reference subject,and a predetermined reference brightness value, and said controllerselects one correction factor among said three types of correctionfactors when making correction of brightness of the image obtained bytaking the X-ray photograph of said reference subject.
 13. The X-raycamera as set forth in claim 1 wherein said correction factor storagemeans stores two types of correction factors corresponding to asoft-tissue equivalent material and a bone-tissue equivalent material bytaking photographs of said two equivalent materials, and said controllerselects one correction factor between said two types of correctionfactors when making correction of brightness of the image obtained bytaking the X-ray photograph of said reference subject.
 14. The X-raycamera as set forth in claim 1, wherein a plurality of X-ray imagesensors are arranged in a manner that a portion of an image-capture areaof each said sensor overlaps with one another, in order to take an X-rayimage of an expanded size without an error of brightness in theoverlapped portion.
 15. The X-ray camera as set forth in claim 1,wherein a thickness of the reference subject is uniform.
 16. The X-raycamera as set forth in claim 1, wherein a material of reference subjectis homogeneous.